Regarding your reply, you shouldn't read into what I wrote that a slightly lower pH with a higher CH is a bad idea. There's a world of difference between theory and practice and the truth is we really don't know. Nevertheless, if you do lower your CH and raise your pH, it will be interesting to see if your pH rise returns -- if it doesn't, then something else happened to explain what you saw. If it does, then we've got a mystery on our hands.

I seriously doubt that near calcium carbonate saturation that any pool sees any sort of serious pH rise because of it. Most well maintained pools saturated in calcium carbonate that have pool covers show virtually no rise in pH and that includes my own pool. It's possible that higher calcium levels may have something to do with carbon dioxide outgassing, but that would be the first time I've heard or read about that. We'll see...

Richard